Insecticides are extensively employed to kill household insects such as the common housefly, cockroaches, and the like. Insecticides which have acquired common usage are conventionally utilized, often from an aerosol container, in the form of aqueous emulsions, aqueous colloidal suspensions, aqueous solutions, or from an organic solvent medium. Normally the use of an aqueous medium is the preferred form from the standpoint of economics and ecological considerations. However, many of the more effective active insecticidal agents are difficultly soluble or not soluble at all in water, and at times cannot be conveniently emulsified in an aqueous medium--at least not to provide a transparent emulsion or an emulsion free from staining or other undesired characteristics including low activity. This has required, therefore, the use of organic solvents as the carrier for the insecticide in certain applications and with certain active insecticidal agents in order to obtain solubility and the essential activity. With other insecticides, because of their insolubility in water and in the commonly employed organic solvents, it has been customary to employ the insecticides as a powder.
More recently, in an effort to provide insecticidal compositions wherein even the most difficultly soluble insecticidal agents are carried in a solvent medium, organic materials having increased solvency power have been selected, included solvents having amphiphilic character, i.e., solvents having both hydrophilic and lipophilic properties; such as 2-pyrrolidone and N-methyl 2-pyrrolidone. In the insecticidal compositions utilizing such solvents, the amphiphilic solvents have been used solely as a solvent for the active insecticidal agent, which materials were primarily used as powders because of their limited solubility. Thus, the amphiphilic solvents have been used primarily with insecticidal agents which were not capable of being solubilized in the more conventional solvent. Note, for example, the disclosure in the Republic of South Africa Application for Pat. No. 695,393 filed July 28, 1969. There is no recognition in the prior art that the aforesaid amphiphilic solvents would provide a beneficial effect such as enhanced activity to the insecticidal formulation.
It is also recognized that in formulating an insecticide, particularly those having household usage such as the Raid.RTM. products manufactured by S. C. Johnson & Son, Inc., Racine, Wis., the assignee of the present application, it is essential not only to provide a formulation providing a high kill of the insects, but it is also essential to have rapid knockdown of the insects. Knockdown, as the term is used herein, is the characteristic of the insecticide whereby the insect, if a flying insect such as a common housefly, is knocked out of the air or, if a crawling insect, is caused to lie dormant giving the appearance of death to the insects, even if not dead. Rapid knockdown is essential in such insecticides since the average user equates the effectiveness of the insecticide with the falling out of the air of a flying insect, such as the common housefly, or with the paralyzing of an insect, if a crawling insect such as the common cockroach, even though the insect, although not knocked down or paralyzed, may die later. To obtain the desired knockdown, it has been necessary to utilize the active insecticidal agent in larger amounts than necessary to obtain a kill. This is undesirable from the standpoint of cost and also from the standpoint of the ecology.
Although the knockdown phenomenon, and the need for knockdown, has long been known, the solutions advanced in the art to obtain rapid knockdown have centered around the use of synergistic combinations of insecticides such as the pyrethrins in combination with piperonyl butoxide wherein one component contributes high kill and the other rapid knockdown, or merely increasing the amount of active ingredient in the formulation. Neither solution is fully satisfactory from the standpoint of, inter alia, cost and the ecology. Accordingly, there is and has been a need for an effective means of providing knockdown power in an insecticidal composition without using large amounts of the insecticidal agent, or combinations of expensive insecticidal agents.